1,1′-binaphthyl, which has a molecular structure composed of two naphthalene skeletons bonded together at their 1-positions, is converted to a 1,1′-binaphthyl derivative in the form of an axially chiral compound by introducing substituents at the 2-position and 2′-position of the skeleton (binaphthyl skeleton) of 1,1′-binaphthyl. Known examples of such a 1,1′-binaphthyl derivative include 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) having diphenylphosphino groups (—PPh2) at the 2-position and 2′-position and 1,1′-bi-2-naphthol (BINOL) having hydroxy groups (—OH) at the 2-position and 2′-position. For example, based on the axial chirality, BINAP and BINOL are used as favorable chiral ligands to transition metals and typical metals in catalytic asymmetric synthesis reactions or in construction of sites for chiral molecular recognition.
Concerning a 1,1′-binaphthyl derivative having alkoxy groups such as methoxy groups or hydroxy groups at the 2-position and 2′-position of the binaphthyl skeleton, there has been an attempt to introduce a substituent at another position of the binaphthyl skeleton. The introduction of a substituent at a position other than the 2-position and 2′-position, coupled with the fact that the alkoxy groups at the 2-position and 2′-position can be converted to hydroxy groups by hydrolysis if necessary, is expected to extend the range of possible applications of binaphthyl derivatives having a BINOL skeleton or a skeleton analogous to BINOL.
Non Patent Literature 1 discloses a method for introducing iodo groups (—I) or pentafluoroethyl groups (—C2F5) at the 3-position, 3′-position, 6-position, and 6′-position of the binaphthyl skeleton of BINOL having hydroxy groups at the 2-position and 2′-position. This method necessarily involves multiple reactions including a protection reaction for protecting the hydroxyl groups with methoxymethyl (MOM) groups and an elimination reaction for eliminating the MOM groups acting as protecting groups and cannot achieve direct introduction of substituents to the skeleton. Non Patent Literature 2 discloses a method for introducing iodo groups (—I) at the 6-position and 6′-position of the skeleton of a 1,1′-binaphthyl derivative having methoxy groups at the 2-position and 2′-position in the presence of a Sc(OTf)3 catalyst.
Patent Literature 1 discloses a method for introducing iodo groups (—I) at the 3-position and 3′-position, or the 3-position, 3′-position, 6-position, and 6′-position of the skeleton of a 1,1′-binaphthyl derivative having methoxy groups at the 2-position and 2′-position in the presence of a Lewis acid. Patent Literature 1 also states that the use of a trifluoromethanesulfonic acid which is a Brønsted acid instead of a Lewis acid fails to allow the substituent introduction reaction to take place.